Best bet Marc is to send a copy to Allan Brandon the North Wales recorder at firstname.lastname@example.orgLooks a bit slim for four-spotted but Allan's best bet.
Marc, your torpedo-shaped larva is of a hawker dragonfly. The larvae of these are active, hence the shape. The angular shape of the head indicates Aeshna sps. I've enhanced the image and can clearly see good lateral spines on abdominal segment 6 and those on s. 9 reach to at least the middle of s.10. The legs are also clearly banded. This indicates Aeshna grandis (Brown Hawker) or possibly A. cyanea (Southern Hawker. Unfortunately, the feature which would separate these (the labial mask), is on the underside of the beast. Would you please let me know where you got the larva from and the date. As you may know, a new atlas of British and Irish dragonflies and damselflies is due out in 2014 and this is the last year to get records to me before it is too late. I'd appreciate anything you could send me from North Wales, including photos for IDing. If you want to be added to the list of people who receive the North Wales Dragonfly Newsletter please let me know. That goes for anyone else out there. If you could use my direct e-mail that would be great: email@example.comThanks,Allan